Thank you all - I found some of the code ref. on this:
NEC 314.17(B)&© **[FONT=Arial,Arial][size=2]The outer jacket of type NM cable shall be secured to the box and extend into the box at least ¼ inch.
[size=3]314.17 Conductors Entering Boxes, Conduit Bodies, or Fittings.
[/FONT]Conductors entering boxes, conduit bodies, or fittings shall be protected from abrasion and shall comply with 314.17(A) through (D).
I couldn’t find all of the code A - D.
I see circuit branch wires entering metal junction boxes, switches, receptacles and panels without connectors often.
Have a blessed day!